The present invention relates to the discovery of novel ligands specific for a receptor from the cannabinoid (CB) receptor family. The invention discloses the discovery of novel ligands specific to this receptor that act as antagonists to the natural ligands for this receptor. The invention also relates to the discovery of novel ligands that act as agonists to the natural ligands for this receptor.
The present invention generally relates to ligands of the mammalian CB receptor family and, more particularly, to cannabidiol and abnormal cannabidiol derivatives that act as antagonists and agonists for non CB1 and non CB2 receptor subgoups and to using these derivatives to treat pathological states arising from abnormal vasoconstriction, blood pressure, and heart rate. The ligands of the present invention elicit beneficial pharmacological effects associated with cannabinoid receptor stimulation without the concomitant psychoactive effects associated with previously described cannabinoid receptor family ligands. Accordingly, the compounds of the present invention provide useful pharmacologic compounds which may be administered to treat various disease states without the deleterious side effects associated with previous cannabinoid receptor compounds. The invention thus also relates to methods for the treatment of disease states which may be alleviated by drug-induced vasodilation such as, e.g., high blood pressure, hypertension, coronary artery disease, and peripheral vascular disease. Additionally, the compounds of the present invention may be utilized in labeled and unlabelled form to identify the non CB1 and non CB2 receptors that are the molecular site(s) of action of these compounds and the parental cannabinoid and abnormal cannabinoid ligands.
Marijuana is a popular recreational drug of abuse because of its psychoactive properties. The major constituent of marijuana is the cannabinoid xcex949-trahydrocannabinol (THC). Naturally occurring cannabinoids may be divided into two categories, plant-derived and endogenous. Plant-derived cannabinoids are known to elicit dramatic psychobehavioral effects and are also known to have complex cardiovascular effects, a prominent component of which is hypotension (Vollmer et al. J. Pharm. Pharmacol. 1974, 26:186-198). Endogenous cannabinoids (endocannabinoids) are a class of lipid-like molecules that share receptor binding sites with plant-derived cannabinoids and mimic many of their neurobehavioral effects (Mechoulam et al. Adv. Exp. Bio. Med. 1996, 402:95-101). Two endocannabinoids have been characterized in some detail: arachidonyl ethanolamide (anandamide) (Devane et al. Science 1992, 258:1946-1949; Felder et al. Proc. Natl. Acad. Sci. USA. 1993, 90:7656-7660) and 2-arachidonyl glyceride (2-AG) (Mechoulam et al. Biochem. Pharmacol 1995, 50:83-90). Like plant-derived cannabinoids, both anandamine and 2-AG are capable of eliciting hypotension (Varga et al. FASEB J. 1998, 12:1035-1044; Varga et al. Eur. J. Pharmacol. 1995, 278:279-283; Stein et al. Br. J. Pharmacol. 1996, 119:107-114; Varga et al. Hypertension 1996, 28:682-688; Lake et al. Hypertension 1997, 29:1204-1210; Calignano et al. Eur. J. Pharmacol. 1997, 337: R1-R2).
Cannabanoids exert their effects by binding to specific receptors located in the cell membrane. To date, two cannabinoid receptors have been cloned, the CB1 receptor expressed primarily in the brain (Matsuda et al. Nature 1990, 346:561-564) but also in some peripheral tissues (Shire et al. J. Biol. Chem. 1995, 270:3726-3731), and CB2 receptors expressed by cells of the immune system (Munro et al. Nature 1993, 365:61-65). Studies with the selective CB1 receptor antagonist SR141716A implicated the CB1 receptor subtype in cannabinoid-induced hypotension and bradycardia (Varga et al. (1995), Eur. J. Pharmacol. 278, 279-283; Lake et al. (1997) J. Pharmacol. Exp. Ther. 281, 1030-1037), a conclusion recently confirmed by the use of mice deficient in CB1 receptors (Ledent et al. (1999) Science 283, 401-404). However, it has recently been reported that in the rat isolated mesenteric arterial bed anandamide elicits prolonged vasodilation partially inhibited by SR141716A, but THC and synthetic agonists highly potent at both CB1 and CB2 receptors, such as HU-210 (17) or WIN 55212-2 (18), do not have a vasodilator effect (Wagner, et al. (1999) Hypotension 33(II);429-434). These findings implicate as-yet unidentified receptor(s) in anandamide-induced mesenteric vasodilation which may be called xe2x80x9cCB1-likexe2x80x9d receptor(s).
Recent findings indicate that the compound xe2x80x9cabnormal cannabidiolxe2x80x9d (Abn-cbd) may be a selective agonist of CB1-like receptors that does not interact with CB1 receptors (Adams et al., Experientia 1977, 33:1204-1205, see also U.S. Pat. No. 5,939,429, which are incorporated herein by reference). In both anesthetized rats and mice, 10 mg/kg (i.v.) of Abn-cbd was found to cause hypotension that could be prevented by pretreatment of the animals with 3 mg/kg SR141716A. Abn-cbd elicited similar although shorter lasting hypotension, inhibited by SR141716A, in CB1 receptor knockout xe2x88x92/xe2x88x92mice. Furthermore, in the perfused rat mesenteric vascular bed preparation (in which potent CB1 agonists were found to be inactive), Abn-cbd caused vasodilation which could be inhibited by SR141716A. These last two findings indicate that Abn-cbd induces hypotension via xe2x80x9cCB1-likexe2x80x9d (non-CB1) cannabinoid receptors. In other experiments it was found that Abn-cbd in doses up to 60 mg/kg does not cause marijuana-like neurobehavioral effects in mice. Furthermore, using an in vitro ligand binding assay Abn-cbd at concentrations up to 100 uM failed to displace a potent known ligand of CB1 receptors from CB1 cannabinoid receptors in a rat brain plasma membrane preparation. These latter findings indicate that Abn-cbd is not an agonist of CB1 receptors. Additional studies have since shown that the vasodilatory effects associated with Abn-cbd are not mediated via binding to CB2 receptors.
In sum, it has been thus far demonstrated that Abn-cbd does not bind to the brain cannabinoid (CB1) receptor and does not elicit cannabinoid-like neurobehavioral effects in rats and mice. However, abn-cbd has been found to lower blood pressure and to dilate isolated mesenteric arteries in normal rats and mice and also in genetically altered mice that do not express CB1 receptors (CB1 knockout mice), or mice that do not express either the CB1 or the CB2 receptor (CB1/CB2 double knockout mice). (Proceedings of the National Academy of Sciences [PNAS], vol. 96, pp. 14136-14142 (1999), which is herein incorporated by reference.). Furthermore, cannabidiol (the parent compound of abn-cbd), which is also devoid of neurobehavioral effects and does not bind to CB1 receptors, does not elicit mesenteric vasodilation but is able to antagonize the vasodilator effect of Abn-cbd (Id. and U.S. Pat. No. 5,939,429).
The vasodilator response to Abn-cbd remains unchanged in the presence of 100 xcexcM NG-nitro-L-arginine methyl ester (L-NAME) and 10 xcexcM indomethacin in the perfusion buffer, which indicates that endothelial NO and cyclooxygenase products such as prostacyclin do not contribute to the response. Also, in the presence of 5 xcexcM capsazepine (Kd at vanilloid VRI receptors: 285 nM), the bolus injection of 4 mg Abn-cbd elicited the same long lasting vasodilation as in its absence. This observation further indicates that inhibition of vasodilation by the Abn-cbd is not attributable to non-specific blockade of vanilloid receptors.
These findings suggest that Abn-cbd and cannabidiol are a selective agonist and antagonist, respectively, of an as yet unidentified cannabinoid-like receptor distinct from CB1 or CB2 receptors. These findings also suggest that agonists of these receptors, such as Abn-cbd, might be useful in the treatment of diseases where drug-induced vasodilation is desirable (e.g. high blood pressure disease or hypertension, coronary artery disease, peripheral vascular disease, abnormal heart rate). The potential usefulness of Abn-cbd may be limited, however, by its relatively low potency, i.e. the need for relatively high doses to elicit vasodilation or to lower blood pressure. Similarly, the inhibitory potency of cannabidiol is also low.
There thus exists a need for analogs of Abn-cbd and cannabidiol that can elicit similar biological activities in smaller doses and thus having a greater potential efficacy in the treatment of pathological states which may benefit from drug-induced regulation of vasodilation.
It is therefore an object of the invention to provide structurally modified analogs of Abn-cbd, with the aim of obtaining compounds with a similar activity profile, but greater potency than Abn-cbd.
It is another object of the invention to provide methods for the stimulation of mesenteric vasodilation by administering to an animal structurally modified analogs of Abn-cbd.
It is another object of the invention to provide methods for the treatment of pathological states by the administration of analogs of Abn-cbd with a concurrent increase in vasodilation yet without psychoactive side effects.
It is another object of the invention to provide structural analogs of cannabidiol with the aim of obtaining compounds with a similar activity profile, but greater potency than cannabidiol yet without psychoactive side effects.
It is another object of the invention to provide methods for the inhibition of mesenteric vasodilation by administering to an animal structurally modified analogs of cannabidiol.
It is another object of the invention to provide methods for the treatment of pathological states by the administration of analogs of cannabidiol and a concurrent inhibition of vasodilation without psychoactive side effects.
It is another object of the invention to provide methods for the treatment of pathological states by the administration of analogs of cannabidiol and Abn-cbd wherein the pathological states include abnormal blood pressure and abnormal heart rate.
It is yet another object of the invention to provide labeled and unlabelled agonists and antagonists that are specific for a non-CB1 and non-CB2 receptors which may be used as tools to characterize and isolate xe2x80x9cCB1-likexe2x80x9d receptors that regulate mesenteric vasodilation in animals.
According to the invention, derivatives of cannabidiol and abnormal cannabidiol are provided which act as agonists or antagonists to cannabidiol or abnormal cannabidiol. The compounds of the present invention are provided as derivatives of Abn-cbd and cannabidiol. They are provided in pharmacologically useful compositions and may be used to regulate mesenteric vasoconstriction, blood pressure, and heart rate through ligand-receptor interaction with CB1-like receptors without a concurrent psychoactive effect.